On the Seasonal Dimorphism of Butterflies. 97 



as heretofore the reproduction of Ascaris nigrove- 

 nosa, of Leptodora appendwilata, and of the cattle- 

 lice, but also that of the Aphides, Coccidce, Daph- 

 nidce, Rotatoria, and Phyllopoda, and, in short, all 

 those cases in which we can determine the former 

 identity of the two kinds of generations from their 

 form, anatomical structure, and mode of reproduc- 

 tion. This conclusion is essentially supported by 

 a comparison of the most closely allied species. 

 Thus, for instance, when we see the genus Aphis 

 and its allies related on all sides to insects which 

 propagate sexually in all generations, and when 

 we further observe the great similarity of the 

 whole external and internal structure in the two 

 kinds of generations of Aphis, we are forced to 

 the conjecture that the apparent asexual repro- 

 duction of the Aphides is in reality partheno- 

 genesis, i. e., that it has been developed from 

 sexual reproduction. Neither can it be any 

 longer disputed that in this case, as well as in that 

 of Leptodora and other Daphnidcz, the same 

 female alternately propagates parthenogenetically, 

 and produces eggs requiring fertilization. This 

 was established by Von Heyden 13 some years 

 ago, in the case of Lachnus Querci, and has been 

 since confirmed by Balbiani. 14 



There can be no doubt that in all these cases 

 the cycle of generations has been developed from 



1 ''Stettin, entom. Zeit, vol. xviii p. 83, 1857. 

 14 Compt. Rend., vol. Ixxvii. p. 1164, 1873. 



H 



